This invention relates to mechanical actuators, and more particularly to mechanical actuators which release the actuated load when the actuator fails.
There are many requirements for mechanical actuators which release the actuated load when the actuator fails, thereby rendering the load free to move (e.g., under the control of another actuator which has not failed). For example, many of the movable flight control surfaces in aircraft are positioned by redundant actuators. If one of these actuators were to fail, it may be vitally important that the failed actuator not lock the associated flight control surface in the position at which that actuator failed. Instead, the failed actuator should leave the associated flight control surface "free" so that it can continue to be moved by the other actuator or actuators which have not failed. Actuators which thus leave the associated load free to move when the actuator fails are sometimes referred to herein as "fail-free" actuators. "Fail-free" does not mean that the actuator cannot fail; it merely means that if the actuator does fail, it does not fix or lock up the load, but rather leaves the load free to move.